Retirement Benefits (Other Postretirement Benefit Plans Changes Recognized in Other Comprehensive Income on Pretax Basis) (Details) - Other Postretirement Benefits Plan - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial (gain) loss arising during the period	$ (10.7)	$ 7.5
Amortization of net actuarial loss	(0.2)	(0.7)
Total	$ (10.9)	$ 6.8